Portal monitoring with steered-beam RFID systems

ABSTRACT

Portals and other chokepoints can be monitored with RFID reader systems. A portion of an RFID reader system capable of generating multiple beams can be mounted between two adjacent chokepoints such that some beams are associated with one chokepoint while other beams are associated with the other chokepoint. When replies from an item are received, the item can be associated with a chokepoint based on parameters or characteristics associated with the replies and/or the beam(s) on which the replies are received. If the detected item is moving, its movement direction through the chokepoint and/or its movement speed may also be determined.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 16/137,555 filed on Sep. 21, 2018, which claims thebenefit of U.S. Provisional Patent Application Ser. No. 62/561,651 filedon Sep. 21, 2017. The disclosures of the above application are herebyincorporated by reference for all purposes.

BACKGROUND

Radio-Frequency Identification (RFID) systems typically include RFIDreaders, also known as RFID reader/writers or RFID interrogators, andRFID tags. RFID systems can be used in many ways for locating andidentifying objects to which the tags are attached. RFID systems areuseful in product-related and service-related industries for trackingobjects being processed, inventoried, or handled. In such cases, an RFIDtag is usually attached to an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to inventoryone or more RFID tags, where inventorying involves using inventoryingcommands to singulate a tag, receive an identifier from a tag, and/oracknowledge a received identifier (e.g., by transmitting an acknowledgecommand). “Singulated” is defined as a reader singling-out one tag,potentially from among multiple tags, for a reader-tag dialog.“Identifier” is defined as a number identifying the tag or the item towhich the tag is attached, such as a tag identifier (TID), electronicproduct code (EPC), etc. The reader transmitting a Radio-Frequency (RF)wave performs the interrogation. The RF wave is typicallyelectromagnetic, at least in the far field. The RF wave can also bepredominantly electric or magnetic in the near or transitional nearfield. The RF wave may encode one or more commands that instruct thetags to perform one or more actions.

In typical RFID systems, an RFID reader transmits a modulated RFinventorying signal (an inventorying command), receives a tag reply, andtransmits an RF acknowledgement signal responsive to the tag reply. Atag that senses the interrogating RF wave may respond by transmittingback another RF wave. The tag either generates the transmitted back RFwave originally, or by reflecting back a portion of the interrogating RFwave in a process known as backscatter. Backscatter may take place in anumber of ways.

The reflected-back RF wave may encode data stored in the tag, such as anumber. The response is demodulated and decoded by the reader, whichthereby identifies, counts, or otherwise interacts with the associateditem. The decoded data can denote a serial number, a price, a date, atime, a destination, an encrypted message, an electronic signature,other attribute(s), any combination of attributes, and so on.Accordingly, when a reader receives tag data it can learn about the itemthat hosts the tag and/or about the tag itself.

An RFID tag typically includes an antenna section, a radio section, apower-management section, and frequently a logical section, a memory, orboth. In some RFID tags the power-management section included an energystorage device such as a battery. RFID tags with an energy storagedevice are known as battery-assisted, semi-active, or active tags. OtherRFID tags can be powered solely by the RF signal they receive. Such RFIDtags do not include an energy storage device and are called passivetags. Of course, even passive tags typically include temporary energy-and data/flag-storage elements such as capacitors or inductors.

RFID systems can be used to track the movement of items through afacility. For example, appropriately positioned and configured RFIDreaders can track the movement and location of items in a warehouse. Ingeneral, different facility layouts and configurations may requiredifferent RFID system configuration in order to provide adequatetracking capability.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

Embodiments are directed to monitoring portals and other chokepointswith RFID reader systems. A portion of an RFID reader system capable ofgenerating multiple beams can be mounted between two adjacent chokepointsuch that some beams are associated with one chokepoint while otherbeams are associated with the other portal. When replies from an itemare received, the item can be associated with a chokepoint based onparameters or characteristics associated with the replies and/or thebeam(s) on which the replies are received. If the detected item ismoving, its movement direction through the chokepoint and/or itsmovement speed may also be determined.

According to one example, a method to track the trajectory of an RFIDtag is provided. The method may include generating a first plurality ofspatially separated reader beams oriented along a first tag trajectoryand generating a second plurality of spatially separated reader beamsoriented along a second tag trajectory. The method may further includetransmitting inventorying commands on the first and second plurality ofreader beams and receiving, from the tag, a plurality of repliesresponding to the inventorying commands. The method may further includedetermining at least one cumulative reply parameter from the pluralityof replies, selecting the first or second tag trajectories as an actualtag trajectory based on the at least one cumulative reply parameter, anddetermining a tag trajectory direction from the at least one cumulativereply parameter.

According to another example, a method for a synthesized-beam reader totrack the trajectory of an RFID tag is provided. The method may includesynthesizing a first plurality of spatially separated beams orientedalong a first tag trajectory and synthesizing a second plurality ofspatially separated beams oriented along a second tag trajectory. Themethod may further include transmitting inventorying commands on thefirst and second plurality of beams and receiving, from the tag, aplurality of replies responding to the inventorying commands. The methodmay further include determining at least one cumulative reply parameterfrom the plurality of replies, selecting the first or second tagtrajectories as an actual tag trajectory based on the at least onecumulative reply parameter, and determining a tag trajectory directionfrom the at least one cumulative reply parameter.

According to yet another example, a method to track the passage of anRFID tag through one of two neighboring portals is provided. The methodincludes generating, via a first RFID reader, a first plurality ofspatially separated beams oriented near a first one of the portals and asecond plurality of spatially separated beams oriented near a second oneof the portals. The method further includes transmitting inventoryingcommands on the first and second plurality of beams and receiving, fromthe tag, a plurality of replies responding to the inventorying commands.The method further includes determining at least one cumulative replyparameter from the plurality of replies and determining that the tag ispassing through the first or second portal in a passage direction.

These and other features and advantages will be apparent from a readingof the following detailed description and a review of the associateddrawings. It is to be understood that both the foregoing generaldescription and the following detailed description are explanatory onlyand are not restrictive of aspects as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description proceeds with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram of components of an RFID system.

FIG. 2 is a diagram showing components of a passive RFID tag, such as atag that can be used in the system of FIG. 1.

FIG. 3 is a conceptual diagram for explaining a half-duplex mode ofcommunication between the components of the RFID system of FIG. 1.

FIG. 4 is a block diagram showing a detail of an RFID reader system,such as the one shown in FIG. 1.

FIG. 5 is a block diagram illustrating an overall architecture of anRFID system according to embodiments.

FIG. 6 depicts a synthesized-beam antenna and synthesized beams orientedin different physical directions, according to embodiments.

FIG. 7 depicts how synthesized-beam readers can be used to detect andinventory items passing through portals, according to embodiments.

FIG. 8 depicts how synthesized-beam readers can be used to detect themotion of items passing through portals, according to embodiments.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments or examples. These embodimentsor examples may be combined, other aspects may be utilized, andstructural changes may be made without departing from the spirit orscope of the present disclosure. The following detailed description istherefore not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

As used herein, “memory” is one of ROM, RAM, SRAM, DRAM, NVM, EEPROM,FLASH, Fuse, MRAM, FRAM, and other similar volatile and nonvolatileinformation-storage technologies as will be known to those skilled inthe art, and may be volatile or not. Some portions of memory may bewriteable and some not. “Command” refers to a reader request for one ormore tags to perform one or more actions, and includes one or more taginstructions preceded by a command identifier or command code thatidentifies the command and/or the tag instructions. “Instruction” refersto a request to a tag to perform a single explicit action (e.g., writedata into memory). “Program” refers to a request to a tag to perform aset or sequence of instructions (e.g., read a value from memory and, ifthe read value is less than a threshold then lock a memory word).“Protocol” refers to a standard for communications between a reader anda tag (and vice versa), such as the Class-1 Generation-2 UHF RFIDProtocol for Communications at 860 MHz-960 MHz by GS1 EPCglobal, Inc.(“Gen2 Specification”), versions 1.2.0 and 2.0 of which are herebyincorporated by reference.

FIG. 1 is a diagram of the components of a typical RFID system 100,incorporating embodiments. An RFID reader 110 transmits an interrogatingRF signal 112. RFID tag 120 in the vicinity of RFID reader 110 sensesinterrogating RF signal 112 and generates signal 126 in response. RFIDreader 110 senses and interprets signal 126. The signals 112 and 126 mayinclude RF waves and/or non-propagating RF signals (e.g., reactivenear-field signals).

Reader 110 and tag 120 communicate via signals 112 and 126. Whencommunicating, each encodes, modulates, and transmits data to the other,and each receives, demodulates, and decodes data from the other. Thedata can be modulated onto, and demodulated from, RF waveforms. The RFwaveforms are typically in a suitable range of frequencies, such asthose near 900 MHz, 13.56 MHz, and so on.

The communication between reader and tag uses symbols, also called RFIDsymbols. A symbol can be a delimiter, a calibration value, and so on.Symbols can be implemented for exchanging binary data, such as “0” and“1”, if that is desired. When symbols are processed by reader 110 andtag 120 they can be treated as values, numbers, and so on.

Tag 120 can be a passive tag, or an active or battery-assisted tag(i.e., a tag having its own power source). When tag 120 is a passivetag, it is powered from signal 112.

FIG. 2 is a diagram of an RFID tag 220, which may function as tag 120 ofFIG. 1. Tag 220 is drawn as a passive tag, meaning it does not have itsown power source. Much of what is described in this document, however,applies also to active and battery-assisted tags.

Tag 220 is typically (although not necessarily) formed on asubstantially planar inlay 222, which can be made in many ways known inthe art. Tag 220 includes a circuit which may be implemented as an IC224. In some embodiments IC 224 is implemented in complementarymetal-oxide semiconductor (CMOS) technology. In other embodiments IC 224may be implemented in other technologies such as bipolar junctiontransistor (BJT) technology, metal-semiconductor field-effect transistor(MESFET) technology, and others as will be well known to those skilledin the art. IC 224 is arranged on inlay 222.

Tag 220 also includes an antenna for exchanging wireless signals withits environment. The antenna is often flat and attached to inlay 222. IC224 is electrically coupled to the antenna via suitable IC contacts (notshown in FIG. 2). The term “electrically coupled” as used herein maymean a direct electrical connection, or it may mean a connection thatincludes one or more intervening circuit blocks, elements, or devices.The “electrical” part of the term “electrically coupled” as used in thisdocument shall mean a coupling that is one or more of ohmic/galvanic,capacitive, and/or inductive. Similarly, the terms “electricallyisolated” or “electrically decoupled” as used herein mean thatelectrical coupling of one or more types (e.g., galvanic, capacitive,and/or inductive) is not present, at least to the extent possible. Forexample, elements that are electrically isolated from each other aregalvanically isolated from each other, capacitively isolated from eachother, and/or inductively isolated from each other. Of course,electrically isolated components will generally have some unavoidablestray capacitive or inductive coupling between them, but the intent ofthe isolation is to minimize this stray coupling to a negligible levelwhen compared with an electrically coupled path.

IC 224 is shown with a single antenna port, comprising two IC contactselectrically coupled to two antenna segments 226 and 228 which are shownhere forming a dipole. Many other embodiments are possible using anynumber of ports, contacts, antennas, and/or antenna segments.

Diagram 250 depicts top and side views of tag 252, formed using a strap.Tag 252 differs from tag 220 in that it includes a substantially planarstrap substrate 254 having strap contacts 256 and 258. IC 224 is mountedon strap substrate 254 such that the IC contacts on IC 224 electricallycouple to strap contacts 256 and 258 via suitable connections (notshown). Strap substrate 254 is then placed on inlay 222 such that strapcontacts 256 and 258 electrically couple to antenna segments 226 and228. Strap substrate 254 may be affixed to inlay 222 via pressing, aninterface layer, one or more adhesives, or any other suitable means.

Diagram 260 depicts a side view of an alternative way to place strapsubstrate 254 onto inlay 222. Instead of strap substrate 254's surface,including strap contacts 256/258, facing the surface of inlay 222, strapsubstrate 254 is placed with its strap contacts 256/258 facing away fromthe surface of inlay 222. Strap contacts 256/258 can then be eithercapacitively coupled to antenna segments 226/228 through strap substrate254, or conductively coupled using a through-via which may be formed bycrimping strap contacts 256/258 to antenna segments 226/228. In someembodiments, the positions of strap substrate 254 and inlay 222 may bereversed, with strap substrate 254 mounted beneath inlay 222 and strapcontacts 256/258 electrically coupled to antenna segments 226/228through inlay 222. Of course, in yet other embodiments strap contacts256/258 may electrically couple to antenna segments 226/228 through bothinlay 222 and strap substrate 254.

In operation, the antenna receives a signal and communicates it to IC224, which may both harvest power and respond if appropriate, based onthe incoming signal and the IC's internal state. If IC 224 usesbackscatter modulation then it responds by modulating the antenna'sreflectance, which generates response signal 126 from signal 112transmitted by the reader. Electrically coupling and uncoupling the ICcontacts of IC 224 can modulate the antenna's reflectance, as canvarying the admittance of a shunt-connected circuit element which iscoupled to the IC contacts. Varying the impedance of a series-connectedcircuit element is another means of modulating the antenna'sreflectance. If IC 224 is capable of transmitting signals (e.g., has itsown power source, is coupled to an external power source, and/or is ableto harvest sufficient power to transmit signals), then IC 224 mayrespond by transmitting response signal 126.

In the embodiments of FIG. 2, antenna segments 226 and 228 are separatefrom IC 224. In other embodiments, the antenna segments mayalternatively be formed on IC 224. Tag antennas according to embodimentsmay be designed in any form and are not limited to dipoles. For example,the tag antenna may be a patch, a slot, a loop, a coil, a horn, aspiral, a monopole, microstrip, stripline, or any other suitableantenna.

An RFID tag such as tag 220 is often attached to or associated with anindividual item or the item packaging. An RFID tag may be fabricated andthen attached to the item or packaging, or may be partly fabricatedbefore attachment to the item or packaging and then completelyfabricated upon attachment to the item or packaging. In someembodiments, the manufacturing process of the item or packaging mayinclude the fabrication of an RFID tag. In these embodiments, theresulting RFID tag may be integrated into the item or packaging, andportions of the item or packaging may serve as tag components. Forexample, conductive item or packaging portions may serve as tag antennasegments or contacts. Nonconductive item or packaging portions may serveas tag substrates or inlays. If the item or packaging includesintegrated circuits or other circuitry, some portion of the circuitrymay be configured to operate as part or all of an RFID tag IC. An “RFIDIC” may refer to an item capable of receiving and responding to RFIDsignals. For example, an item having a separate but attached RFID tagcan be considered an RFID IC, as is an item having an integrated RFIDtag or an item manufactured to have the capabilities of an RFID tag. Astandalone RFID tag may also be referred to as an “RFID IC”.

The components of the RFID system of FIG. 1 may communicate with eachother in any number of modes. One such mode is called full duplex, whereboth reader 110 and tag 120 can transmit at the same time. In someembodiments, RFID system 100 may be capable of full duplex communicationif tag 120 is configured to transmit signals as described above. Anothersuch mode, suitable for passive tags, is called half-duplex, and isdescribed below.

FIG. 3 is a conceptual diagram 300 for explaining half-duplexcommunications between the components of the RFID system of FIG. 1, inthis case with tag 120 implemented as passive tag 220 of FIG. 2. Theexplanation is made with reference to a TIME axis, and also to a humanmetaphor of “talking” and “listening”. The actual technicalimplementations for “talking” and “listening” are now described.

RFID reader 110 and RFID tag 120 talk and listen to each other by takingturns. As seen on axis TIME, when reader 110 talks to tag 120 thecommunication session is designated as “R→T”, and when tag 120 talks toreader 110 the communication session is designated as “T→R”. Along theTIME axis, a sample R→T communication session occurs during a timeinterval 312, and a following sample T→R communication session occursduring a time interval 326. Interval 312 may typically be of a differentduration than interval 326—here the durations are shown approximatelyequal only for purposes of illustration.

According to blocks 332 and 336, RFID reader 110 talks during interval312, and listens during interval 326. According to blocks 342 and 346,RFID tag 120 listens while reader 110 talks (during interval 312), andtalks while reader 110 listens (during interval 326).

In terms of actual behavior, during interval 312 reader 110 talks to tag120 as follows. According to block 352, reader 110 transmits signal 112,which was first described in FIG. 1. At the same time, according toblock 362, tag 120 receives signal 112 and processes it to extract dataand so on. Meanwhile, according to block 372, tag 120 does notbackscatter with its antenna, and according to block 382, reader 110 hasno signal to receive from tag 120.

During interval 326, which may also be referred to as a backscatter timeinterval or backscatter interval, tag 120 talks to reader 110 asfollows. According to block 356, reader 110 transmits a continuous wave(CW) signal, which can be thought of as a carrier that typically encodesno information. This CW signal serves both to transfer energy to tag 120for its own internal power needs, and also as a carrier that tag 120 canmodulate with its backscatter. Indeed, during interval 326, according toblock 366, tag 120 does not receive a signal for processing. Instead,according to block 376, tag 120 modulates the CW emitted according toblock 356 so as to generate backscatter signal 126, for example byadjusting its antenna reflectance. Concurrently, according to block 386,reader 110 receives backscatter signal 126 and processes it.

FIG. 4 is a block diagram of an RFID reader system 400 according toembodiments. RFID reader system 400 includes a local block 410, andoptionally remote components 470. Local block 410 and remote components470 can be implemented in any number of ways. For example, local block410 or portions of local block 410 may be implemented as a standalonedevice or as a component in another device. In some embodiments, localblock 410 or portions of local block 410 may be implemented as a mobiledevice, such as a handheld RFID reader, or as a component in a mobiledevice, such as a laptop, tablet, smartphone, wearable device, or anyother suitable mobile device. It will be recognized that RFID reader 110of FIG. 1 is the same as local block 410, if remote components 470 arenot provided. Alternately, RFID reader 110 can be implemented instead byRFID reader system 400, of which only the local block 410 is shown inFIG. 1.

In some embodiments, one or more of the blocks or components of readersystem 400 may be implemented as integrated circuits. For example, localblock 410, one or more of the components of local block 410, and/or oneor more of the remote component 470 may be implemented as integratedcircuits using CMOS technology, BJT technology, MESFET technology,and/or any other suitable implementation technology.

Local block 410 is responsible for communicating with RFID tags. Localblock 410 includes a block 451 of an antenna and a driver of the antennafor communicating with the tags. Some readers, like that shown in localblock 410, contain a single antenna and driver. Some readers containmultiple antennas and drivers and a method to switch signals among them,including sometimes using different antennas for transmitting and forreceiving. Some readers contain multiple antennas and drivers that canoperate simultaneously. In some embodiments, block 451 may be aphased-array antenna or synthesized-beam antenna (SBA), described inmore detail below, and local block 410 may be implemented in asynthesized-beam reader (SBR) configured to generate one or more beamsvia the SBA. A demodulator/decoder block 453 demodulates and decodesbackscattered waves received from the tags via antenna/driver block 451.Modulator/encoder block 454 encodes and modulates an RF wave that is tobe transmitted to the tags via antenna/driver block 451.

Local block 410 additionally includes an optional local processor 456.Local processor 456 may be implemented in any number of ways known inthe art. Such ways include, by way of examples and not of limitation,digital and/or analog processors such as microprocessors anddigital-signal processors (DSPs); controllers such as microcontrollers;software running in a machine such as a general purpose computer;programmable circuits such as Field Programmable Gate Arrays (FPGAs),Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices(PLDs), Application Specific Integrated Circuits (ASIC), any combinationof one or more of these; and so on. In some cases, some or all of thedecoding function in block 453, the encoding function in block 454, orboth, may be performed instead by local processor 456. In some cases,local processor 456 may implement an encryption or authenticationfunction; in some cases, one or more of these functions can bedistributed among other blocks such as encoding block 454, or may beentirely incorporated in another block.

Local block 410 additionally includes an optional local memory 457.Local memory 457 may be implemented in any number of ways known in theart, including, by way of example and not of limitation, any of thememory types described above as well as any combination thereof. Localmemory 457 can be implemented separately from local processor 456, or inan IC with local processor 456, with or without other components. Localmemory 457, if provided, can store programs for local processor 456 torun, if needed.

In some embodiments, local memory 457 stores data read from tags, ordata to be written to tags, such as Electronic Product Codes (EPCs), TagIdentifiers (TIDs) and other data. Local memory 457 can also includereference data that is to be compared to EPCs, instructions and/or rulesfor how to encode commands for the tags, modes for controlling antenna451, encryption/authentication algorithms, algorithms for tracking taglocation or movement, secret keys, key pairs, individual public and/orprivate keys, electronic signatures, and so on. In some of theseembodiments, local memory 457 is provided as a database.

Some components of local block 410 typically treat the data as analog,such as the antenna/driver block 451. Other components such as localmemory 457 typically treat the data as digital. At some point, there isa conversion between analog and digital. Based on where this conversionoccurs, a reader may be characterized as “analog” or “digital”, but mostreaders contain a mix of analog and digital functionality.

If remote components 470 are provided, they are coupled to local block410 via an electronic communications network 480. Network 480 can be aLocal Area Network (LAN), a Metropolitan Area Network (MAN), a Wide AreaNetwork (WAN), a network of networks such as the internet, or a localcommunication link, such as a USB, PCI, and so on. Local block 410 mayinclude a local network connection 459 for communicating withcommunications network 480 or may couple to a separate device orcomponent configured to communicate with communications network 480.Communications on the network can be secure, such as if they areencrypted or physically protected, or insecure if they are not encryptedor otherwise protected.

There can be one or more remote component(s) 470. If more than one, theycan be located at the same location, or in different locations. They maycommunicate with each other and local block 410 via communicationsnetwork 480, or via other similar networks, and so on. Accordingly,remote component(s) 470 can use respective remote network connections.Only one such remote network connection 479 is shown, which is similarto local network connection 459, etc. In some embodiments, a single oneof the remote component(s) 470 may be configured to communicate withand/or control multiple local blocks, each similar to local block 410.

Remote component(s) 470 can also include a remote processor 476. Remoteprocessor 476 can be made in any way known in the art, such as wasdescribed with reference to local processor 456. Remote processor 476may also implement an encryption/authentication function and/or a taglocation/tracking function, similar to local processor 456.

Remote component(s) 470 can also include a remote memory 477. Remotememory 477 can be made in any way known in the art, such as wasdescribed with reference to local memory 457. Remote memory 477 mayinclude a local database, and a different database of a standardsorganization, such as one that can reference EPCs. Remote memory 477 mayalso contain information associated with commands, tag profiles, keys,or the like, similar to local memory 457.

One or more of the above-described elements may be combined anddesignated as operational processing block 490. Operational processingblock 490 includes those components that are provided of the following:local processor 456, remote processor 476, local network connection 459,remote network connection 479, and by extension an applicable portion ofcommunications network 480 that links remote network connection 479 withlocal network connection 459. The portion can be dynamically changeable,etc. In addition, operational processing block 490 can receive anddecode RF waves received via antenna/driver 451, and causeantenna/driver 451 to transmit RF waves according to what it hasprocessed.

Operational processing block 490 includes either local processor 456, orremote processor 476, or both. If both are provided, remote processor476 can be made such that it operates in a way complementary with thatof local processor 456. In fact, the two can cooperate. It will beappreciated that operational processing block 490, as defined this way,is in communication with both local memory 457 and remote memory 477, ifboth are present.

Accordingly, operational processing block 490 is location independent,in that its functions can be implemented either by local processor 456,or by remote processor 476, or by a combination of both. Some of thesefunctions are preferably implemented by local processor 456, and some byremote processor 476. Operational processing block 490 accesses localmemory 457, or remote memory 477, or both for storing and/or retrievingdata.

RFID reader system 400 operates by operational processing block 490generating communications for RFID tags. These communications areultimately transmitted by antenna/driver block 451, withmodulator/encoder block 454 encoding and modulating the information onan RF wave. Then data is received from the tags via antenna/driver block451, demodulated and decoded by demodulator/decoder block 453, andprocessed by operational processing block 490.

Embodiments of an RFID reader system can be implemented as hardware,software, firmware, or any combination. Such a system may be subdividedinto components or modules. Some of these components or modules can beimplemented as hardware, some as software, some as firmware, and some asa combination. An example of such a subdivision is now described,together with the RFID tag as an additional module.

FIG. 5 is a block diagram illustrating an overall architecture of anRFID system 500 according to embodiments. RFID system 500 may besubdivided into modules or components, each of which may be implementedby itself or in combination with others. In addition, some of them maybe present more than once. Other embodiments may be equivalentlysubdivided into different modules. Some aspects of FIG. 5 are parallelwith systems, modules, and components described previously.

An RFID tag 503 is considered here as a module by itself. RFID tag 503conducts a wireless communication 506 with the remainder, via the airinterface 505. Air interface 505 is really a boundary, in that signalsor data that pass through it are not intended to be transformed from onething to another. Specifications as to how readers and tags are tocommunicate with each other, for example the Gen2 Specification, alsoproperly characterize that boundary as an interface.

RFID system 500 includes one or more reader antennas 510, and an RFfront-end module 520 for interfacing with reader antenna(s) 510. Thesecan be made as described above.

RFID system 500 also includes a signal-processing module 530. In oneembodiment, signal-processing module 530 exchanges waveforms with RFfront-end module 520, such as I and Q waveform pairs.

RFID system 500 further includes a physical-driver module 540, which isalso known as a data-link module. In some embodiments, physical-drivermodule 540 exchanges bits with signal-processing module 530.Physical-driver module 540 can be the stage associated with the framingof data.

RFID system 500 additionally includes a media access control module 550.In one embodiment, media access control layer module 550 exchangespackets of bits with physical driver module 540. Media access controllayer module 550 can make decisions for sharing the medium of wirelesscommunication, which in this case is the air interface.

RFID system 500 moreover includes an application-programminglibrary-module 560. This module 560 can include application programminginterfaces (APIs), other objects, etc.

All of these RFID system functionalities can be supported by one or moreprocessors. One of these processors can be considered a host processor.Such a host processor might include a host operating system (OS) and/orcentral processing unit (CPU), as in module 570. In some embodiments,the processor is not considered as a separate module, but one thatincludes some of the above-mentioned modules of RFID system 500. In someembodiments, the one or more processors may perform operationsassociated with retrieving data that may include a tag public key, anelectronic signature, a tag identifier, an item identifier, and/or asigning-authority public key. In some embodiments, the one or moreprocessors may verify an electronic signature, create a tag challenge,and/or verify a tag response.

User interface module 580 may be coupled toapplication-programming-library module 560, for accessing the APIs. Userinterface module 580 can be manual, automatic, or both. It can besupported by the host OS/CPU module 570 mentioned above, or by aseparate processor, etc.

It will be observed that the modules of RFID system 500 form a chain.Adjacent modules in the chain can be coupled by appropriateinstrumentalities for exchanging signals. These instrumentalitiesinclude conductors, buses, interfaces, and so on. Theseinstrumentalities can be local, e.g. to connect modules that arephysically close to each other, or over a network, for remotecommunication.

The chain is used in one direction for receiving RFID waveforms and inthe other direction for transmitting RFID waveforms. In receiving mode,reader antenna(s) 510 receives wireless waves, which are in turnprocessed successively by the various modules in the chain. Processingcan terminate in any one of the modules. In transmitting mode, waveforminitiation can be in any one of the modules. Ultimately, signals arerouted to reader antenna(s) 510 to be transmitted as wireless waves.

The architecture of RFID system 500 is presented for purposes ofexplanation, and not of limitation. Its subdivision into modules neednot be followed for creating embodiments. Furthermore, the features ofthe present disclosure can be performed either within one of themodules, or by a combination of them. In some embodiments RFID system500 can be incorporated into another electronic device such as acheckout terminal in a store or a consumer device such as a mobilephone.

As described above, synthesized-beam RFID readers (SBRs) may be used forportal monitoring. An SBR can generate multiple radio frequency (RF)beams, and may be formed by coupling one or more RFID readers (ordistributed portions of one or more readers) to antenna elements in asynthesized-beam antenna.

FIG. 6 depicts a synthesized-beam antenna (SBA) 600 with discreteradiating elements suitable for an SBR according to embodiments. SBA 600includes an array of antenna elements 602 and 604, and a ground plane608 behind elements 602 and 604. Each element has a radiating directionvector 606 (only shown for one element) that is typically, but notnecessarily, perpendicular to the ground plane. An RF radiation pattern(or “beam”) for receiving or transmitting an RF signal may besynthesized by adjusting the amplitude and/or phase of the signalscoupled from/to each antenna element 602 and 604. The orientation ordirection of the synthesized beam (typically represented by thedirection of the beam's primary lobe—the lobe having the highestradiated power) is controlled by these various amplitude and/or phaseadjustments. The adjustments may be analog, digital, or a mix of analogand digital. For example, during transmission, an SBR may generate theanalog signal to be transmitted, split the signal, and then direct thesplit signals to elements 602 and 604 with different amplitudes andphases. Alternatively, the SBR may synthesize different signals for eachantenna element digitally and then convert the digital signals toanalog. In some embodiments, each antenna element can be implemented asa separate digital transceiver having its own analog front end. Controlsignals to generate a beam can then be supplied to the different digitaltransceivers, each of which converts a digital signal into an analogsignal for transmission. When the digital transceivers transmit theiranalog signals, the signals combine to form the synthesized beam. Inother embodiments, the SBR may use a mix of these approaches. Similarly,during a receive operation the SBR may combine analog signals afterappropriate phase shifting and amplitude adjustment of each, or it maydigitize the signals from each element and combine them digitally, or amix thereof. In some embodiments, each element of an SBA may be orcoupled to a separate reader. The different readers may then coordinatewith each other (for example, via communications over a network) togenerate beams. In this situation, the system with the multiple readers,each associated with an antenna element, may be referred-to as an SBR.

The antenna elements of SBA 600 may be one or more of patch, slot, wire,horn, helical, distributed, or any other type as will be known to thoseskilled in the art. Whereas FIG. 6 only shows nine antenna elements,antenna arrays with any number of antenna elements may be used,including a single distributed element or an element made frommetamaterials. In some embodiments ground plane 608 may be nonplanar(e.g., curved, concave, convex, etc.) and in other embodiments need notexist.

Diagrams 630 and 660 show the directions of some of the RF beams thatSBA 600 can generate. SBA 600 has nine antenna elements 632-648, withelement 632 at the center and elements 634-648 around it. The shape anddirection of the beam that SBA 600 generates depends on the signalsto/from each element. Suppose that SBR 600 transmits using primarilyelements 632, 636, and 644. Then, depending on the amplitude and phaseof the signals applied to these elements, SBA 600 can change theorientation of a beam (also referred to as “steering” the beam) alongthe direction indicated by dashed line 650. In a similar fashion,suppose that SBR 600 transmits primarily using elements 632, 638, and646. Then, depending on the amplitude and phase of the signals appliedto these elements, SBA 600 can steer a beam along the directionindicated by dashed line 652. Of course, other steering arrangements arepossible, including using all 9 elements to transmit and/or receive inarbitrary directions and to generate narrow beams.

Diagram 660 shows how RF beams with different directions can besynthesized using antenna elements located along line 650, with thediagram to the left depicting a head-on view similar to diagram 630 andthe diagram to the right depicting a side view. As described above, thebeam direction can be controlled by varying the amplitude and phase ofthe signals to/from the antenna elements. For example, by applying aleading signal phase to element 636, an intermediate signal phase toelement 632, and a trailing signal phase to element 644, the SBA willtend to steer its beam downward as in beam 666. Switching leading andlagging from elements 636/644 to elements 644/636 will tend to steer thebeam upwards as in beam 662. Of course, the actual beam shape depends onboth the magnitude of the phase shifting and the magnitude of theamplitude scaling (if any).

A beam can be characterized by one or more longitudinal beamcross-sections (that is, cross-sections of the beam in one or moreplanes parallel to the beam direction) and/or perpendicular beamcross-sections (that is, cross-sections of the beam in one or moreplanes perpendicular to the beam direction). A beam can also becharacterized by a beam length indicative of the power distribution ofthe beam along the beam direction, a beam width indicative of the powerdistribution of the beam in a direction perpendicular to the beamdirection, and/or any other suitable shape-based parameter. Beam shapesmay be based on, for example, the type of antenna used, the RF frequencyof the beam, the power used to generate the beam, and/or how the beam istransmitted. In synthesized-beam embodiments, the beam illumination maybe based on the arrangement of excited antenna elements and theamplitude, phase, and/or frequency of the various signals used to excitethe antenna elements.

Each beam generated by an SBR or any antenna element or combination ofantenna elements has a coverage volume, also known as the beam's“field-of-view”, which is a volume in three-dimensional space where,during transmission, the transmitted energy density exceeds a threshold,and where, during receiving, the received energy density exceeds athreshold. Different beams may have different fields-of-view and mayalso overlap with each other to some degree. A beam's coverage area is aprojection of the beam's field-of-view on a surface, may be of anysuitable shape, and may vary based on interactions between the differentelements that generate the beam, as well as the orientation and topologyof the surface on which the coverage area is projected. Thefield-of-view and coverage area may be different during transmit andreceive, and may vary with reader or tag power, the thresholds, thedistance between the SBR and the surface, and other parameters. Forexample, a beam may have different fields-of-view and therefore coverageareas based on the threshold(s) selected for transmitted and/or receivedenergy densities.

An SBR may be configured to switch between different individual beamsbased on a desired beam scanning timing or pattern. For example, an SBRmay generate a first beam at a first time for a first time-duration,then may switch to generating a second, different beam at a second timefor a second time-duration, and so on. The order, timing, andtime-durations with which an SBR switches between generating differentbeams may be predefined or dynamic. In one embodiment, an SBR may switchbetween different beams based on a predefined schedule and scan pattern.In another embodiment, an SBR may dynamically determine the beams togenerate, the times when they should be generated, and the timedurations for which they should be generated based on environmental orother conditions (e.g., the actual or estimated number of tags present,actual or predicted tag movement patterns, RF interference,environmental noise, or any other suitable condition or parameter). Inother embodiments, an SBR may generate beams by dynamically adjusting apredefined schedule and scan pattern based on environmental conditions.An SBR may be configured to switch beams to optimize the number of tagsinventoried, optimize the ability to detect fast-moving tags, or beconfigured to provide any desired performance metric.

RFID systems can be used to track the passage of items throughchokepoints, such as hallways or portals. For example, an RFID readerpositioned to inventory tagged items passing through a loading dockportal can track the transition of tagged pallets or items through theportal. However, in situations where multiple chokepoints are present,an RFID reader tracking items passing through one chokepoint maymistakenly detect items passing through other chokepoints. For example,an RFID reader configured to track items passing through a first loadingdock portal may inadvertently inventory items passing through a second,adjacent loading dock portal and mistakenly determine that those itemspassed through the first loading dock portal.

In some embodiments, RFID reader systems capable of generating differentbeams, such as reader systems with SBRs or with multiple readers orantennas, can (a) reduce the inadvertent inventorying of items passingthrough other portals and/or (b) be configured to track items passingthrough multiple, adjacent portals.

FIG. 7 depicts how synthesized-beam readers can be used to detect andinventory items passing through portals, according to embodiments.Diagrams 700 and 750 are front and top views, respectively, of adjacentportals 702 and 704. The portals 702 and 704 are configured to allowpallets, such as pallets 706 and 708, to pass through. SBRs 710, 720,and 730 are mounted in “overhead offset” positions in which each reader“looks down” on the space in front of the portals 702/704 such that onlya subset of beams from each SBR have fields-of-view that overlap thespace in front of each portal. For example, SBR 710 is configured togenerate beams 712 and 714 that are oriented toward and overlap thespace in front of portal 702 and portal 704, respectively. SBR 720 isconfigured to generate beams 722 that are oriented toward and overlapthe space in front of portal 702 (depicted in diagram 700 but not indiagram 750), and SBR 730 is configured to generate beams 732 that areoriented toward and overlap the space in front of portal 704 (alsodepicted in diagram 700 but not in diagram 750). Beams 712 and 722 canbe used to determine the location and movement (e.g., trajectories,trajectory directions, and/or trajectory speeds) of items passing intoand out of portal 702, while beams 714 and 732 can be used to determinethe location and movement of items passing into and out of portal 704.

The SBRs 710, 720, and 730 may each independently determine their ownbeam scanning/switching patterns (as described above) or may be part ofa reader system with a centralized or distributed controller thatdetermines the beam scanning/switching pattern for the SBRs. In thelatter case, the controller functionality may be distributed amongprocessors at two or more different SBRs, implemented at a singleprocessor associated with a specific SBR, or implemented at a processorcoupled to the SBRs.

When an SBR such as SBRs 710, 720, or 730 transmits inventoryingcommands and receives replies from a tagged item responding to theinventorying commands, a tracking application coupled to the SBR may usethe replies to estimate a location of the detected item. The trackingapplication may be implemented in hardware and/or software, and may beimplemented at a particular SBR, at a separate processor coupled to theSBRs, or distributed across different SBRs and/or processors.

When SBR 710 receives replies from a tagged item responding topreviously transmitted inventorying commands, the coupled trackingapplication can identify the beam on which the item was detected andthen determine whether the item is more likely to be associated withportal 702 or portal 704. For example, the tracking application candetermine whether replies from an item were received on a beam in beams712 or beams 714. If the replies were received via a beam in beams 712,then the tracking application may determine that the item is associatedwith portal 702. On the other hand, if the replies were received via abeam in beams 714, then the tracking application may determine that theitem is associated with portal 704. Similarly, the tracking applicationmay be able to associate a detected item with a particular portal basedon the beams from SBRs 720 and 730 on which the item is detected. Forexample, the tracking application may associate an item whose replieswere received on beams 722 from SBR 720 with portal 702, and thetracking application may associate an item whose replies were receivedon beams 732 from SBR 730 with portal 704. Accordingly, the trackingapplication can use beams from SBRs 710, 720, and 730 to differentiatebetween items passing through portal 702 and items passing throughportal 704.

In some embodiments, the tracking application may estimate the locationof a detected item using cumulative reply parameters associated withreplies received from the item. A reply parameter associated with anitem may be an individual reply from the tag to a reader command or aparameter associated with the reply, such as received signal strengthindication (RSSI), reply power, reply angle-of-arrival, reply phase,reply contents, or similar. A cumulative reply parameter associated withthe item is the combination of reply parameters over multiple repliesfrom the item. Cumulative reply parameters may be reply counts,cumulative reply RSSIs, cumulative reply power, averageangle-of-arrival, average phase, or similar.

The reply count of an item on a beam refers to the number of times areply is received from the item on that beam over a time duration orwindow. Reply count may also be equivalently expressed as an item replyrate, which is the reply count divided by the relevant time window. Insome embodiments, individual item reply counts or rates may be adjustedor scaled differently based on the situation.

The RSSI of a reply from an item is an indication of the strength of thereply signal, and the tracking application may determine an RSSI foreach reply from the item received on a certain beam and combine theRSSIs for all the replies from the item received on the beam to generatea cumulative reply RSSI for the item on that beam. The power of a replyfrom an item is related to the RSSI for that reply and can be calculatedby appropriate conversion of the reply RSSI. For example, the trackingapplication may determine an RSSI for each reply from the item receivedon a certain beam, convert the RSSI to a reply power, and combine thereply powers to form a cumulative reply power. Alternatively, thetracking application may generate a cumulative reply RSSI as describedabove and then convert the cumulative reply RSSI to a cumulative replypower. The tracking application may combine the RSSIs and powers usingany suitable technique (e.g., addition, multiplication, or similar), andmay scale individual RSSIs or powers differently based on the situation.

The angle-of-arrival of a reply is a measure of the angle between areceiver of the reply and the originator of the reply. Theangle-of-arrival of a reply can be computed based on the timingdifference between when the reply is received at a first receiver andwhen the reply is received at a second receiver. For example, if thefirst receiver receives the reply before the second receiver does, thenthe originator of the reply is closer to the first receiver, assumingthat the reply propagates at a similar speed to both receivers. Theangle-of-arrival of the reply can then be estimated based on the timingdifference and the spatial separation of the receivers. The signal phaseof a backscattered reply may be used to determine a phase differencebetween the backscattered reply and the transmitted signal used for thebackscatter. The phase difference may provide information about thedistance between a receiver and the reply originator. In someembodiments, phase differences at two different receivers may be used todetermine an angle-of-arrival, as described above.

In one embodiment, the tracking application may estimate item locationbased on the highest cumulative reply parameter. For example, thetracking application may identify the beam having the highest replycount, reply rate, cumulative reply RSSI, and/or cumulative reply power,and estimate that the item is at the location or portal associated withthe identified beam.

In some embodiments, the tracking application may estimate item locationbased on a combination of cumulative reply parameter values. Forexample, the tracking application may combine the cumulative replyparameter values for multiple beams associated with a single location(e.g., the beams in beams 712, associated with portal 702) to estimatewhether an item is at the location. As another example, the trackingapplication may form a ratio of two cumulative reply parameter values,each corresponding to a different beam or location, to determine thelikelihood that an item is at each location. In this example, the largerthe ratio of the two cumulative reply parameter values, the more likelythat the item is in the beam or at the location represented by thecumulative reply parameter value in the numerator of the ratio.Similarly, the smaller the ratio, the more likely that the item is inthe beam or at the location represented by the cumulative replyparameter value in the denominator of the ratio.

In some embodiments, the tracking application may use replyangles-of-arrival and/or signal phases to estimate the item location.For example, the tracking application may use angles-of-arrival and/orsignal phases from multiple replies from an item to triangulate ortrilaterate the item. The tracking application may also combine two ormore of the above parameters to refine the item location estimation. Forexample, after identifying a beam based on highest cumulative replyparameter, the tracking application may use angle-of-arrival or phase todetermine whether the replies mostly originate from the beam's main lobe(pointed in the beam's nominal direction), from a side lobe (pointedaway from the beam's nominal direction) of the beam, or from reflectionsfrom the environment or another beam entirely. If theangle-of-arrival/phase indicates that the replies originate from sidelobes or are caused by reflection, then the tracking application maydetermine that the item is not at the location associated with the beam.

RFID systems can also be configured to determine whether a detected itemis moving, and if so, its trajectory, trajectory direction, andtrajectory speed. The item's trajectory represents the physicallocations, route, course, or path of the item over time. The item'strajectory direction indicates the direction of item movement along theitem trajectory, and the item's trajectory speed indicates how fast theitem is moving in the trajectory direction along the item trajectory.

FIG. 8 depicts how synthesized-beam readers can be used to detect themotion of items passing through portals, according to embodiments. FIG.8 depicts top-down views of adjacent portals 802 and 804 and pallets 806and 808 at a time 800 and at a subsequent time 850. Beams 812-826,generated by an RFID system having at least one SBR (e.g., similar toSBR 710), are configured to monitor RFID-tagged items passing into andout of portals 802 and 804. Pallets 806 and 808 are tagged or holdtagged items, and can therefore be read or inventoried by beams 812-826if within range.

At time 800, pallet 806 is moving toward portal 802, and a trackingapplication operative in the RFID system receives replies from pallet806 on beams 812 and 814, but not on any other beams. Beams 812 and 814are near but not at portal 802. Accordingly, the tracking applicationcan use the location estimation described above to determine that attime 800 pallet 806 is near but not at portal 802. Also at time 800,pallet 808 is moving through portal 804, and the tracking applicationreceives replies from pallet 808 on beams 820 and 822, but not on anyother beams. Beams 820 and 822 at least partially overlap portal 804.Accordingly, the tracking application can use the location estimationdescribed above to determine that at time 800 pallet 808 is at portal804.

Subsequently, pallet 806 continues moving to portal 802 and pallet 808continues moving through and away from portal 804. At time 850, thetracking application continues to receive replies from pallet 806 onbeam 814, but no longer on beam 812. In addition, the trackingapplication now receives replies from pallet 806 on beams 816 and 818,at least partially overlapping portal 802. Accordingly, the trackingapplication can use the location estimation described above to determinethat at time 850 pallet 806 is at portal 802. Furthermore, because thetracking application knows the location of pallet 806 at times 800 and850, the tracking application can further determine pallet 806's speedand direction of travel (e.g., away from beam 812 and toward beam 818,or toward portal 802).

Similarly, at time 850 the tracking application continues to receivereplies from pallet 808 on beam 822, but no longer on beam 820. Inaddition, the tracking application now receives replies from pallet 808on beams 824 and 826, near but not at portal 804. Accordingly, thesystem tracking application can determine that (a) at time 850 pallet808 is no longer at portal 804, (b) the direction of travel of pallet808 (e.g., away from beam 820 and toward beam 826, or away from portal804), and (c) the travel speed of pallet 808.

In some embodiments, RF interferers and reflectors in the environmentcan reflect or otherwise propagate RF energy from a beam to a locationoutside the beam field-of-view, thereby creating spurious replies fromitems outside the beam field-of-view and causing errors in the itemlocation and trajectory estimation process. The tracking application mayalleviate the effect of such spurious replies by, for example, removingspurious replies, averaging or accumulating replies over time, and/orusing a ratio of cumulative reply parameter values, as described above.

In some embodiments, the tracking application removes spurious replies.Spurious replies may have reply parameter values that differsignificantly from non-spurious replies. For example, a spurious replymay have significantly lower signal power, significantly different RSSI,different angle-of-arrival, or otherwise appear as an outlier withrespect to other received replies. The tracking application may removespurious replies explicitly, for example by determining that a reply isspurious and discarding it. In some embodiments, the significantdifferences of spurious replies as compared to non-spurious replies makespurious replies appear as high-frequency features as a function oftime, and the tracking application may filter spurious replies out, forexample by using a low-pass filter to remove high-frequency featurescorresponding to spurious replies.

The tracking application may average or accumulate replies over time,such that spurious replies are outnumbered by non-spurious replies. Inthis situation, the reply parameter values of the non-spurious repliesdominate, thereby reducing the error due to spurious replies in thelocation estimation process.

The tracking application may use a ratio of cumulative reply parametervalues to alleviate the effect of spurious replies. For example, supposethat the tracking application receives replies from pallet 806 on beam812 and beam 816. The tracking application may compute cumulative replyparameters for pallet 806 for both beams and generate a ratio of thecumulative reply parameters. Suppose that the ratio has the cumulativereply parameter for beam 812 as its numerator and the cumulative replyparameter for beam 816 as its denominator. If the ratio is relativelyclose to one, then the tracking application may not be able to determinewhether pallet 806 is more closely associated with beam 812 or beam 816,although in some embodiments, the tracking application may assume thatpallet 806 is equally associated with both beams (in other words,located between both beams). If the ratio is significantly less thanone, then the tracking application may determine that pallet 806 is atthe location associated with beam 816, with a confidence based on howclose the ratio is to zero (or how far the ratio is from one).Similarly, if the ratio is significantly greater than one, then thetracking application may determine that pallet 806 is at the locationassociated with beam 812, with a confidence based on how much larger theratio is than one. In some embodiments, the ratio may be converted toany other suitable scale as desired. For example, the ratio may beconverted to a scale such that an unconverted ratio value of “one” isconverted to a value of “zero”. In this situation, using the ratiodescribed above as an example, if the converted ratio is significantlygreater than zero the tracking application may determine that pallet 806is at the location associated with beam 812, whereas if the convertedratio is significantly less than zero the tracking application maydetermine that pallet 806 is at the location associated with beam 816.

The tracking application may also use cumulative reply parameter ratiosto determine when and in what direction an item such as pallet 806 hastransitioned through a chokepoint such as portal 802. For example,suppose the cumulative reply parameter ratio is as described above, withthe numerator representing beam 812 and the denominator representingbeam 816. If pallet 806 is moving through portal 802 in the directiondepicted in FIG. 8, then the cumulative reply parameter ratio will havea first, large value and will fall to a second value significantly lessthan zero during the movement. If pallet 806 were moving in the oppositedirection, then the ratio would have a first value significantly lessthan zero and rise to a second, large value. Accordingly, the trackingapplication can determine an item's passage direction through achokepoint based on the direction or sign of the change in or differencebetween a first ratio and a second, subsequent ratio.

The tracking application may estimate whether an item has transitionedthrough any chokepoints before attempting to identify the specificchokepoint through which the item has transitioned. For example, thetracking application may determine, for a detected item, a firstcumulative reply parameter ratio where the numerator represents allbeams near but not at chokepoints (e.g., beams 812, 814, 824, and 826)and the denominator represents all beams at chokepoints (e.g., beams816, 818, 820, and 822). The tracking application then uses the firstcumulative reply parameter ratio to determine whether the item hastransitioned any chokepoint (e.g., either portal 802 or portal 804) andthe direction of the transition. Subsequently, or in parallel, thetracking application may then attempt to identify the specificchokepoint through which the item has transitioned.

The tracking application may deem that a transition through a chokepointis valid (i.e., has probably occurred) if either a difference betweenthe first and second cumulative reply parameter ratio values or thesecond ratio value satisfy certain thresholds, which may be differentdepending on the transition direction. For example, the trackingapplication may use a first ratio or ratio difference value threshold todetermine if pallet 806 is moving through portal 802 as depicted in FIG.8. On the other hand, the tracking application may use a second ratio orratio difference value threshold if pallet 806 were moving the oppositeway. In some embodiments, the tracking application may also require thata valid transition satisfy the threshold for some minimum time, toalleviate ephemeral effects such as those from spurious replies. Thethreshold may be an unsigned magnitude, which can be satisfiedregardless of the direction of the change or the sign of the ratio, ormay be a signed magnitude, which can only be satisfied by a change inthe corresponding direction or a ratio with the appropriate sign.

The valid transition of an item through a chokepoint may be used todetermine whether other item transitions through chokepoints are valid.For example, suppose a tracking application identifies a validtransition of a first item through a first chokepoint in a firstdirection. If the first item is associated with other items (e.g., otheritems within the same pallet as the first item), then the trackingapplication may determine that it is relatively more likely that theother items will also transition through the first chokepoint in thefirst direction at that time. Accordingly, the tracking application mayreduce the thresholds used to validate transitions through the firstchokepoint in the first direction around the time of the first item'stransition, to account for the increased probability of transition andto capture as many potentially transiting items as possible.Subsequently, the tracking application may increase the thresholds totheir former levels or even higher to reduce the likelihood of falsealarms. In some embodiments, the tracking application may validatetransitions for items identified as associated with the first item(e.g., items known to be previously on the same pallet as the firstitem) using the reduced thresholds, but validate transitions for otheritems not identified as associated with the first item (e.g., items notpreviously on the same pallet as the first item or on entirely differentpallets) using unreduced thresholds.

FIG. 8 depicts beams from a single SBR/SBA, but in other embodimentsbeams from other SBRs or SBAs can be used to locate and track taggeditems. For example, beams from SBRs or SBAs mounted on the far sides ofportals 802 and 804 (similar to the SBRs depicted in FIG. 7) can beused, in conjunction with beams 812-826, to locate and track pallets 806and 808.

In some embodiments, beams from readers or antennas not explicitlyassociated with a chokepoint may also be used in the item location andtrajectory estimation techniques described above. For example, afacility may include readers that generate beams configured to trackitem location or movement within the facility. Suppose replies from anitem are received on such beams. A tracking application may thendetermine that the item is within the facility. Suppose then a potentialchokepoint transition of the item is detected. If the detectedtransition is into the facility, and a previous transition of the itemout of the facility was not detected, the tracking application mayignore that transition or flag that transition as erroneous, because theitem was already determined to be within the facility. If the detectedtransition is out of the facility and replies from the item aresubsequently received on beam(s) outside the facility, then the trackingapplication has additional confidence that the detected transition iscorrect. On the other hand, if the detected transition is out of thefacility and replies from the item are subsequently received on beam(s)within the facility, then the tracking application may ignore thattransition or flag that transition as erroneous, because the item isstill within the facility.

While monitoring is described above in the context ofoverhead-offset-mounted SBRs, in other embodiments SBRs or SBAs can bemounted in other ways. For example, an overhead SBR or SBA can bemounted directly above a chokepoint such that its beams only cover thechokepoint, or can cover multiple chokepoints. As another example, anSBR or SBA can be mounted between two adjacent chokepoints and orientedhorizontally and away from the two chokepoints, such that some beamscover the approach to one chokepoint and other beams cover the approachto the other chokepoint. Similarly, an SBR or SBA can be orientedhorizontally between two adjacent chokepoints and toward the chokepointssuch that some beams are directed toward and into one chokepoint andother beams are directed toward and into the other chokepoint. In somesituations, an SBR or SBA can be mounted such that its beams cover morethan two chokepoints.

In some embodiments, item location and trajectory estimation may involvethe use of cooperative powering, as described in copending andcommonly-owned U.S. patent application Ser. No. 16/023,719, filed onJun. 29, 2018 and hereby incorporated by reference in its entirety. Inthese embodiments, multiple beams from multiple readers, such as beams712 and beams 722 from SBRs 710 and 720, may cooperate as described inthe above-referenced application to increase inventorying range andavailable power.

In other embodiments, non-synthesized-beam reader systems capable ofgenerating multiple beams can be used to implement item location andtrajectory estimation. For example, a reader coupled to multipleantennas can generate multiple beams, and the antennas can be mounted toprovide patterns of beams suitable for implementing item location andtrajectory estimation. Similarly, a reader system with multiple,single-beam readers can generate multiple beams, and the readers can bemounted to provide patterns of beams suitable for implementing itemlocation and trajectory estimation. In general, reader systems capableof generating spatially separated beams, which are beams withfields-of-view that do not entirely overlap, can be used to implementthe item location and trajectory estimation techniques described herein.In some embodiments, reader systems capable of generating beams withdifferent fields-of-view, some of which are entirely encompassed byother beams, can also be used to implement the item location andtrajectory estimation techniques described herein.

As mentioned previously, embodiments are directed to using RFID systemsto estimate item location and trajectory through portals or otherchokepoints. Embodiments additionally include programs, and methods ofoperation of the programs. A program is generally defined as a group ofsteps or operations leading to a desired result, due to the nature ofthe elements in the steps and their sequence. A program is usuallyadvantageously implemented as a sequence of steps or operations for aprocessor, but may be implemented in other processing elements such asFPGAs, DSPs, or other devices as described above.

Performing the steps, instructions, or operations of a program requiresmanipulating physical quantities. Usually, though not necessarily, thesequantities may be transferred, combined, compared, and otherwisemanipulated or processed according to the steps or instructions, andthey may also be stored in a computer-readable medium. These quantitiesinclude, for example, electrical, magnetic, and electromagnetic chargesor particles, states of matter, and in the more general case can includethe states of any physical devices or elements. It is convenient attimes, principally for reasons of common usage, to refer to informationrepresented by the states of these quantities as bits, data bits,samples, values, symbols, characters, terms, numbers, or the like. Itshould be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities, and that theseterms are merely convenient labels applied to these physical quantities,individually or in groups.

Embodiments furthermore include storage media. Such media, individuallyor in combination with others, have stored thereon instructions, data,keys, signatures, and other data of a program made according to theembodiments. A storage medium according to the embodiments is acomputer-readable medium, such as a memory, and is read by a processorof the type mentioned above. If a memory, it can be implemented in anyof the ways and using any of the technologies described above.

Even though it is said that the program may be stored in acomputer-readable medium, it should be clear to a person skilled in theart that it need not be a single memory, or even a single machine.Various portions, modules or features of it may reside in separatememories, or even separate machines. The separate machines may beconnected directly, or through a network such as a local access network(LAN) or a global network such as the Internet.

Often, for the sake of convenience only, it is desirable to implementand describe a program as software. The software can be unitary, orthought of in terms of various interconnected distinct software modules.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams and/orexamples. Insofar as such block diagrams and/or examples contain one ormore functions and/or aspects, it will be understood by those within theart that each function and/or aspect within such block diagrams orexamples may be implemented individually and/or collectively, by a widerange of hardware, software, firmware, or virtually any combinationthereof. Those skilled in the art will recognize that some aspects ofthe RFID embodiments disclosed herein, in whole or in part, may beequivalently implemented employing integrated circuits, as one or morecomputer programs running on one or more computers (e.g., as one or moreprograms running on one or more computer systems), as one or moreprograms running on one or more processors (e.g. as one or more programsrunning on one or more microprocessors), as firmware, or as virtuallyany combination thereof, and that designing the circuitry and/or writingthe code for the software and/or firmware would be well within the skillof one of skill in the art in light of this disclosure.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, configurations, antennas, transmission lines, and the like,which can, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations).

Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, and C”would include but not be limited to systems that have A alone, B alone,C alone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

As will be understood by one skilled in the art, for any purpose, suchas in terms of providing a written description, all ranges disclosedherein also encompass any and all possible subranges and combinations ofsubranges thereof. Any listed range can be easily recognized assufficiently describing and enabling the same range being broken downinto at least equal halves, thirds, quarters, fifths, tenths, etc. As anon-limiting example, each range discussed herein can be readily brokendown into a lower third, middle third and upper third, etc. As will alsobe understood by one skilled in the art all language such as “up to,”“at least,” “greater than,” “less than,” and the like include the numberrecited and refer to ranges which can be subsequently broken down intosubranges as discussed above. Finally, as will be understood by oneskilled in the art, a range includes each individual member. Thus, forexample, a group having 1-3 cells refers to groups having 1, 2, or 3cells. Similarly, a group having 1-5 cells refers to groups having 1, 2,3, 4, or 5 cells, and so forth.

We claim:
 1. A Radio Frequency Identification (RFID) system configured to identify a chokepoint through which an RFID tag is transitioning, the system comprising: a controller communicatively coupled to one or more readers and configured to control an operation of the one or more readers; a first reader configured to: generate, based on instructions received from the controller, a first plurality of spatially separated reader beams oriented toward a first chokepoint and a second plurality of spatially separated reader beams oriented toward a second chokepoint different from the first chokepoint; transmit inventorying commands on the first and second plurality of reader beams; receive, from the RFID tag, a plurality of replies responding to at least some of the inventorying commands; and transmit the plurality of replies to the controller, wherein the controller is further configured to: determine, from the plurality of replies, at least one cumulative reply parameter; select, based on the at least one cumulative reply parameter, one of the first and second chokepoints as the chokepoint through which the RFID tag is transitioning; and determine, from the at least one cumulative reply parameter, a transition direction for the RFID tag through the selected chokepoint.
 2. The system of claim 1, wherein the at least one cumulative reply parameter is based on a reply count or a cumulative reply power.
 3. The system of claim 2, wherein the controller is further configured to derive the cumulative reply power from a plurality of received signal strength indications associated with the plurality of replies.
 4. The system of claim 1, wherein the controller is further configured to: determine, for at least two reader beams oriented toward the selected chokepoint, respective beam cumulative reply parameters; compute, based on the beam cumulative reply parameters, first and second cumulative reply parameter ratios; and determine the transition direction by: identifying a difference between the first and second cumulative reply parameter ratios; and determining the transition direction based on the difference.
 5. The system of claim 1, wherein the first plurality of spatially separated reader beams are oriented toward the first chokepoint and the second plurality of spatially separated reader beams are oriented toward the second chokepoint simultaneously.
 6. The system of claim 1, further comprising a second reader configured to generate a third plurality of reader beams oriented toward the first chokepoint; wherein the inventorying commands are transmitted on the first, second, and third plurality of reader beams.
 7. The system of claim 6, wherein the controller is integrated with at least one of the first reader and the second reader.
 8. A Radio Frequency Identification (RFID) system employing synthesized-beam readers (SBRs) to track a passage of tags through two neighboring chokepoints, the system comprising: a controller; and a first SBR communicatively coupled to the controller, wherein the first SBR comprises: a synthesized beam antenna (SBA); a transceiver coupled to the SBA; and a processor coupled to the transceiver, the processor configured to: synthesize a first plurality of spatially separated beams oriented toward a first chokepoint; synthesize a second plurality of spatially separated beams oriented toward a second chokepoint; transmit inventorying commands on the first and second plurality of beams; receive, from a first RFID tag and a second RFID tag, a plurality of replies responding to at least some of the inventorying commands; and provide the received plurality of replies to the controller, wherein the controller is further configured to: determine, from the plurality of replies, at least a first cumulative reply parameter for the first RFID tag and a second cumulative reply parameter for the second RFID tag; determine, based on at least the first and the second cumulative reply parameters, that the first and second RFID tags are simultaneously passing through the first and second chokepoints, respectively; and determine, based on at least the first and the second cumulative reply parameters, that the first RFID tag is passing through the first chokepoint in a first direction and the second RFID tag is passing through the second chokepoint in a second direction.
 9. The system of claim 8, wherein the first cumulative reply parameter is based on a reply count of the first RFID tag.
 10. The system of claim 8, wherein the first cumulative reply parameter is based on a cumulative reply power of the first RFID tag.
 11. The system of claim 10, wherein the controller is further configured to derive the first cumulative reply power from a plurality of received signal strength indications associated with the plurality of replies.
 12. The system of claim 8, wherein the controller is further configured to: determine, for at least two beams oriented toward the first chokepoint, respective beam cumulative reply parameters; compute, based on the beam cumulative reply parameters, first and second cumulative reply parameter ratios; and determine that the first RFID tag is passing through the first chokepoint in the first direction by: identifying a difference between the first and second cumulative reply parameter ratios; and determining the first direction based on the difference.
 13. The system of claim 8, further comprising: another reader comprising: another transceiver; and another processor coupled to the other transceiver, the other processor configured to generate a third plurality of beams oriented toward the first chokepoint; and wherein the inventorying commands are transmitted on the first, second, and third plurality of beams.
 14. A Radio Frequency Identification (RFID) system to track the passage of an RFID tag through one of two neighboring portals, the system comprising: a first RFID reader; a second RFID reader; a third RFID reader; and a controller communicatively coupled to the first, second, and third RFID readers, wherein the controller is configured to: cause both the first RFID reader and the second RFID reader to generate a first plurality of spatially separated beams oriented toward a first one of the portals; cause both the second RFID reader and the third RFID reader to generate a second plurality of spatially separated beams oriented toward a second one of the portals; cause inventorying commands to be transmitted on the first and second plurality of beams; receive, from the RFID tag, a plurality of replies responding to at least some of the inventorying commands; determine, from the plurality of replies, at least one cumulative reply parameter; select, based on the at least one cumulative reply parameter, one of the first and second portals as the portal through which the RFID tag is passing; and determine, based on the at least one cumulative reply parameter, a passage direction for the RFID tag through the selected portal.
 15. The system of claim 14, wherein the at least one cumulative reply parameter is based on a reply count or a cumulative reply power.
 16. The system of claim 15, wherein the controller is further configured to derive the cumulative reply power from a plurality of received signal strength indications associated with the plurality of replies.
 17. The system of claim 14, wherein the controller is a distributed controller and is integrated with one or more of the first, second, and third RFID readers.
 18. The system of claim 14, wherein the controller is further configured to: determine, for at least two beams in one of the first and second plurality of beams, respective beam cumulative reply parameters; compute, based on the beam cumulative reply parameters, first and second cumulative reply parameter ratios; and determine the passage direction based on a difference between the first and second cumulative reply parameter ratios.
 19. The system of claim 14, wherein: the first RFID reader is disposed on a side of the first portal opposite the second RFID reader and the second RFID reader is disposed between the first and second portals; and the third RFID reader is disposed on a side of the second portal opposite the second RFID reader.
 20. The system of claim 14, wherein at least one of the first, second, and third RFID readers is a synthesized-beam reader (SBR). 